1. Field of the Invention
The present invention generally relates to an acousto-optical modulator (AOM), a method of making the AOM, and an arrangement for and a method of adjusting laser beam power using the AOM, especially for use in a color image projection system operative for projecting a two-dimensional image in color while maintaining low power consumption, high resolution, miniature compact size, quiet operation and minimal vibration.
2. Description of the Related Art
It is generally known to project a two-dimensional image on a screen based on a pair of scan mirrors which oscillate in mutually orthogonal directions to scan a laser beam over a raster pattern. However, the known image projection systems project the image with limited resolution, typically less than a fourth of video-graphics-array (VGA) quality of 640×480 pixels, and not in true color.
To obtain a true color image, red, blue and green lasers are required to be pulsed at frequencies on the order of 100 MHz. Currently available red and blue lasers can be pulsed at such high frequencies, but the currently available green lasers cannot. As a result, an acousto-optical modulator (AOM) is used to high frequency modulate the intensity of the green laser beam emitted by the green laser. Typically, the AOM includes a crystal through which the green beam passes, an acoustic transducer for producing acoustic waves in the crystal to produce a modulated output beam, and a matching network for impedance matching an acoustic drive signal to the transducer.
However, the physical size of the known AOMs is relatively large, thereby rendering them impractical for use in miniature, hand-held, battery-operated applications. For example, the matching network and the crystal are typically mounted in spaced apart relation to each other on a common heat sink. Also, it is cumbersome to adjust the position of the known AOMs relative to the laser beam, because an optical bench of substantial size and having multiple freedoms of movement is required. The known matching networks also use manually tunable components, which contribute to a high assembly cost.